This invention relates to an apparatus for finishing synthetic polymers, and more particularly, it relates to an apparatus having vertical screw elements which fully wipe the interior surfaces of the finisher apparatus.
U.S. Pat. No. 3,717,330 issued to Pinney discloses a separator-finisher apparatus suitable for use in the production of synthetic condensation polymers such as polyamides and polyesters. The apparatus disclosed in the patent includes a vessel having an interior surface throughout its vertical length in the shape of two intersecting conical frustums with parallel and substantially vertical axes, the bases of the frustums being displaced upwards with respect to the apexes, two interengaging helical screw elements rotatably mounted within the vessel which upon co-rotation conform to the interior surface of the vessel such that the screw elements effect a complete wiping of the interior surface of the vessel, and the screw elements interengage each other uninterruptedly along their lengths such that each element effects a complete wiping of an adjacent element. The term "wiping" as used herein means relative motion between two elements in close and uniform proximity such that a liquid in the clearance between the elements is subject to high shear. The entire disclosure of the Pinney patent is incorporated herein by way of reference.
When such an apparatus is used for the preparation of polymers, such as poly(hexamethylene adipamide), thermal degradation and gelation tends to occur in stagnant regions of the processing vessel, such as when generated suspended molten polymer particles (aerosols) deposit on conduit surfaces above the vent opening and drain by gravity to the vent edge where stalactites form and dangle into the process stage. These stalactites, which are degraded overage material, periodically break off into the melt pool below and contaminate the process.